The present invention relates to a method for tracing a line image in an image processor and, more particularly, to a method for tracing a line image in an image processor such as a CAD (computer-aided design) apparatus, adapted to trace the line image on an interactive basis.
Heretofore, a method for entering drawings written on paper into a graphics processing system has generally involved entering the drawings as image data with an image scanner or the like, displaying the image data on a display through the graphics processing system, and tracing the image data manually through a pointing device or the like by the operator.
For example, a conventional method for entering drawings on an interactive basis, as described in Japanese Patent Laid-open Publication (Kokai) No. 269,276/1987, involves entering the drawings into a computer through a scanner as image data, displaying the image data on the display screen so as to be superimposed on center line image data, and entering the drawings as vector data by indicating the necessary positions on the drawings displayed on the display screen through a coordinate indicator.
As described hereinabove, for example, when the image data are converted into graphic data such as vector data, center data of the center (or the center line) of the image are determined and data on necessary characteristic points of the image, such as end points, branch points, corner points, and the like, from the continuous center line of the center data are selected, specified and entered. In entering the characteristic points, the image data are displayed so as to be superimposed on the center data on the display screen in order for the operator to readily determine the characteristic points, and the characteristic points are then entered by instructions to enter by the operator. Hence, this method suffers from the disadvantage that the data on the display screen becomes so complex that the operator may feel it difficult to select necessary data efficiently.
Further, when the image data are converted into graphics data such as vector data, a data image of line graphics may be given from contour data of the image without processing into small lines. This technology is proposed in Japanese Patent Laid-open Publication (Kokai) No. 117,374/1985, entitled "Method for Approximating Polygonal Lines of Line Graphics". In this proposed technology, contour data should be given for all image data in converting the line image from the contour data into line graphics.
In addition, an image processor has been developed which is provided with a semi-automatic image trace processing function so as to trace image points semi-automatically, determine the characteristic points, and enter graphic data on the characteristic points. In converting the line image into line graphics semi-automatic through such a semi-automatically image trace processing function of the image processor, the contour data for the whole drawing are required to be given as a pre-processing for converting the line image into the line graphics from the contour data as in the method for approximating the polygonal lines of line graphics.
When the semi-automatic trace processing of the line image in the image data by the aid of the semi-automatic image trace processing function of such an image processor is applied to image data of a map, the image data to be converted into graphics data by the operator represent roads, configurations of the ground, and the like, and symbols, characters and the like are not required to be converted into the graphics data.
In the trace processing, the operator is required to always pay attention to one location in the semi-automatic image tracing system in which the operator is inquired as to which way to proceed; however, in the method of approximating the polygonal lines of the line graphics, the contour data are required to be given for all the drawings as the pre-processing, so that this method wastes time.